Patients with homozygous familial hypercholesterolemia (HFH) have been treated by monthly plasma exchange to lower plasma cholesterol concentrations. One patient who was treated for 22 months had resolution of xanthomas but died during cardiac surgery. Plasma exchange was abandoned in the second patient, a retarded 17 year old girl, because of her refusal to take medications or follow dietary advice. The third patient, a 38 year old woman, has had marked resolution of cutaneous xanthomas and improvement in her exercise tolerance.